This led officers to fire numerous rounds into Palczynski, killing him.
More than anything else, it is sheer ambition that leads undercover officers to their line of work.
Then in November, a terrified teenager, saying he had been tortured, led officers to the home of a 29-year-old man.
Officer Rivera began cooperating with investigators, her lawyer said, and led officers to a gun in her backyard.
He fled, leading other officers on a chase that ended when he crashed his car and was slightly injured.
He would later lead officers to the spot where he had disposed of her body.
He said he did not know what led officers to search El-Amin.
He then led officers on a chase over several rooftops, the police said.
Not far from that spot were several other bloodstains, which formed a trail that eventually led officers to the roof.
A police dog led officers to the house, a few blocks away.