//------------------------------//
// III - Obviously 
// Story: A Study in Amber 
// by Time Ponies are cool 
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III - Obviously
The first thing Eagle did was to observe the side of the road. He stopped me before I could take another step away from the cab and then proceeded to walk up and down the road for a few meters with his eyes scrutinizing every detail of the ground beneath his hooves. He then moved on to the walkway leading to the front stairs. He crouched down with his head close to the ground and observed the dirt path. He then left the path and walked onto the grass. He walked across the lawn and then turned to investigate the grass to the right of the house. He made a full circle around the house doing exactly that, while occasionally looking up at the building itself, before he finally returned to me and nodded, indicating that could I continue forward.
As Eagle made his curious first investigations, the policepony standing by the front door went inside the house, presumably to inform whoever was in charge that the consulting detective had arrived. The griffin who came to our flat earlier then came out to greet him by stairs. He was wearing a coverall.
"You found an assistant that quickly?" the griffin asked.
"He was readily available," Eagle replied. He stepped aside to briefly introduce me, "This is Dr. Greenheart."
The griffin held out his claw, which I accepted and we shook hoof and claw. He introduced himself as, "Detective Inspector LeGrande."
Before I had the chance to say, "Pleasure to meet you," Eagle walked with the D.I. back into the house to get straight to business.
"So, tell me about the victim."
"Cloud Puff. Female. Pegasus. Forty-seven years old. 1.35 meters. No occupation. Married to Cotton Puff, a female Earth Pony, works as a gardener. Cotton Puff disappeared the night of the murder. No murder weapon found. Same pattern as all the others. An elderly neighbor noticed that nopony in the house stirred at the usual time and she suspected something was wrong, so she called the police to investigate. When an officer came - the same officer stationed at the door - he found Cloud Puff dead. We've been working here since noon."
The three of us walked down the narrow central corridor of the house. As I looked to the left and right I found a sitting room, a bathroom, a flight of stairs, and a closet. 
"And the house has been on constant surveillance since the body was discovered?" Eagle continued as we were walking.
"Oui," the D.I. answered, "Nopony but us have been in or out of the house since we arrived."
The corridor led to the kitchen, where a few investigation personnel went about, all in coveralls. The kitchen was rather brightly colored compared to the rest of the house. The walls were covered in wallpaper with rows of fruits and vegetables. The windows were blocked by yellow curtains and the floor was of white linoleum. There were counters, a stove, a sink, a refrigerator, cupboards and so on. It was just like a regular kitchen, except for the dead body lying on its side  at the center of the floor, with a few feathers scattered about. This must have been the late Cloud Puff, a skinny, light-blue-coated, red-maned mare with a cutie mark of a pair of knitting needles.
One of the ponies investigating the kitchen looked up from scrutinizing the floor and saw us arrive at the doorway. He grabbed a pair of coveralls and a few pairs of latex gloves and approached us. He had a dark green coat, a short neatly-cut dark brown mane and orange eyes.
"You and your special somepony better use these, Freak," he said as he tossed the scrub suits at us. He spoke with in a scornful tone that showed his contempt for Eagle Eye. "I don't want you contaminating the evidence."
"Shut up, Sour Lime," Eagle replied, "I wear a coverall when I want to wear a coverall, not when you tell me to."
"You can't even legally be here. It's against regula-"
"Lime, just let him in!" LeGrande interrupted, "Eagle Eye has full access to the scene. Let him be."
Quietly, but sorely, Sour Lime stepped aside, and Eagle, after putting on a pair of gloves,  immediately circled around the kitchen, his head calmly turning to and fro, and his eyes darting in all directions as he - I presumed - observed every detail of the room. He briefly stopped in front of the sink, which contained a pile of dishes, before he quickly turned and kneeled down beside the body. He reached his right hoof into his curly mane and pulled out a small compact magnifying glass. Using it, he looked over the poor mare, first at her bloodied wound, then her face, her mane, and her hooves. Then he stood back up.
He turned his head to me, saying, "Doctor, examine the wound. I need your input."
"Excuse me?" I quickly answered in surprise.
"You're my assistant, doctor. Go examine the body, if you please."
"Um, alright."  I put on a coverall and gloves, approached the body and looked at the stab wound on her chest.
As I made my examination, Eagle said, "The other three victims were stabbed in the back. All were married and lived alone with their spouses in their homes and those spouses promptly disappeared the night of each murder. All but this one were stabbed in the back and the wounds could be clearly identified as a knife for the first two victims and a unicorn horn for the third. This victim obviously saw her killer approach and reacted by turning around and-"
"What? That's ridiculous!" Sour Lime interrupted, "How can you even be sure she turned around?"
"Lime, do shut up. You're lowering the I.Q. of the room and you know how I despise rooms full of more stupid than usual. Obviously she turned around and struggled, otherwise the murderer would have had an easy kill by stabbing her in the back without any fuss, just like in the other three. It's little more than common sense. So, the victim was stabbed in the chest, and by a very strange weapon, or more likely a very strange horn. Now, Doctor, you've seen that wound before haven't you?"
Gravely, and with some struggle over the hard memories the wound brought back, I answered, "Yes."
"Where?"
"Canterlot. On the bodies of my friends who were killed in the Changeling invasion."
"And that confirms my hypothesis," Eagle decisively said, "This mare, as well as all the other victims, were murdered, not by their spouses, but by changelings. And, another obvious detail, the murderer is still here in this house, or rather, out by the front door."
Everypony's eyes quickly widened, a few gasped, and all turned around and looked down the corridor and out the door at the solitary policepony, who had overheard everything Eagle just said, staring back at them with a horrified look on his face. As the murdered stood there with his legs shivering, LeGrande calmly said, "Get him."
Sour Lime stepped forward and galloped down the corridor. The murderer took a few quick frightened steps back and then fell over as he backed into the porch stairs. Fortunately for him, Sour Lime stepped on part of his scrub suit, tripped and landed on his face.
LeGrande grunted in frustration as he watch the murderer take the opportunity to turn and run. He ripped off his scrub suit and shouted, "Mon dieu! Must I do all the chasing myself!" He ran down the corridor, opened his wings and flew off after the changeling, who by now probably returned to its original form and started flying away. 
LeGrande left behind him an awkward silence. Sour Lime groaned as he got himself back up and rubbed his face. Eagle smirked. He took the gloves off his hooves and said, "One step closer to solving this mystery." Then he turned and walked down the corridor towards the front door. I took of my gloves and coverall and tried to walk as fast as my leg brace would allow me so as to catch up with my enigmatic flatmate.
"Care to explain all that, Eagle?" I said as we walked down the dirt walkway.
"All the evidence I really needed is right beneath your hooves, doctor. The rest was more for confirmation than anything else."
I looked down at the dirt and could not make out what on earth he mean. "And that evidence would be...?"
"There is no branch of detective science which is so important and so much neglected as the art of tracing hoofsteps."
"You mean to say you figured all that out from looking at hoofsteps?"
"Goodness, you lot are dull. So much information can be found in places you don't even think to look and often that information is the most valuable."
We reached the street and Eagle took a sharp turn to the left, making his way towards a more heavily trafficked street where there would be cabs. Above us clouds had begun to blanket the sky but the late afternoon sun still shone in a clear area. Fortunately a row of tall office buildings kept it from shining at my eyes. I looked at my watch and saw that we spent no more than ten minutes in the house. I followed Eagle's lead and listened to his explanation.
"The murder took place at five o'clock this morning, four hours before the body was discovered at nine o'clock. That was eleven hours ago. Earlier, it rained heavily between one o'clock and two o'clock. The hoofprints on the dirt path and the yard could only have formed between the time the ground dried enough to maintain its shape - which would have been around four o'clock - and now. Since the location was closed off and kept under surveillance from the time of the discovery, the hoofprints must belong to the following: the Puffs, the police, the investigation team and the murderer."
"Hold on," I interrupted, "How'd you know it rained at those exact times? You would've been sleeping."
"I don't sleep. Not when I have more interesting things to do. Now, as I was saying, the prints on the path would have been made only by those ponies. It was easy for me to tell which were made by the police since they have to wear specific horseshoes as part of their uniforms, and I can tell which were made by the Trotland Yard personnel since they were the most recent and were formed at the same time as LeGrande's distinctive claw-prints and paw-prints. Any unfamiliar prints would therefore belong to the Puffs and the murderer. But despite the fact that there weren't that many policeponies and investigators causing disturbances on the path, I could not find the slightest trace of other prints - not even any that would have formed while the ground was wet and easily stood out - meaning nopony had walked on that path between the time the rain ended and the discovery of the body. 
"The grass surrounding the house indicates the same thing. Because the murder was not too long ago, any disturbances in the grass at that time would still remain - the grass would not have had the time to fully stand back up, especially given its length. From looking around the house, I found no flattened or disturbed grass whatsoever. So, nopony had walked there either since the rain ended. We can eliminate flight as a way to enter the house, as the windows were locked, none were broken and all were ridiculously dusty. If any of them were opened, the dust would have been disturbed, but there was no indication of that. The back door was locked and when we passed through the front door, I saw that it was broken open - obviously not by the murderer, but by the police officer. If the murderer broke the door open, the Puffs would have heard, and so would their neighbors most likely. So the door was locked when the officer arrived at the house. 
"Now, we can easily conclude that the murderer had been in the house for a long time, at the very least ever since it was raining. And, even more interesting, he hadn't left the house."
We arrived at a main road, Stirrup Lane, and Eagle began waving for a cab, all the while rambling on about his deductions. An old brown cab approached and stopped in front of us. The driver's left hoof splashed into a puddle at the side of the road. "Where to, mate?" he asked
"Trotland Yard Headquarters, please," Eagle said. He opened the cab door and hopped in. I followed, taking a seat across from him.
"Will do," the driver replied as he pulled away from the curb, "Get you there in fifteen."
We entered the traffic of Londerby's streets again. Why we were heading to Trotland Yard, I did not know. My best guess was that he had more investigating to do. He took out his jar of zap apple jam (though I had no idea where he took it from) and looked at it intently as he continued on speaking.
"I came to the same conclusion in all the other cases. The unique details of this one help me with the next question, which, of course, is 'who.' The first clue was the numbers. They didn't match up. Judging from the hoofprints, four police ponies went to the house and four left. Five Trotland Yard personnel went to the house and four were there when we arrived. At this point I was almost certain there was an impostor, most likely a changeling. After all, the Changeling invasion was defeated by blasting the creatures out of Canterlot and scattering them across Equestria. Some were bound to end up in somepony's home in Londerby."
"How do the numbers not match?" I asked, "Four to four and five to five."
"Four police ponies came and four left. So how could there have been one standing by the front door?"
My eyes widened as I realized this. "Oh..." The devil truly was in the details. I put some thought into it and then asked, "But what if the impostor was one of the police who left?"
"Don't be daft, Greenheart," Eagle replied with a hint of annoyance, "The impostor couldn't have been the one who left. Everypony would have noticed that there were two of the same pony at the scene. The better question is: what happened to the real  officer? If he continued on, going his merry way with the rest of the police, somepony would have noticed that one of him was at a crime scene while another was sipping hot chocolate at Doughnut Joe's. What happened to the spouses of the victims, for that matter? In addition to that, we have to ask, why did these murders happen? Why did the changelings turn against their spouses - off of whose love they feed on - and kill them? Why did the other three changelings use a weapon instead of their horn? In the other cases, the changeling fled from the scene, but this one stayed. Why? Solving one question merely opens up more and it's our job to solve them."
"I'm sorry. 'Our'?"
"You agreed to be my assistant, so you'll continue to assist me. This mystery used to be a simple string of murders, but now it's turned into something deeper and much more fun. The plot thickens."