Omaha, Neb. ? Omaha police say they now know the cause of death for a man suspected of shooting another to death north of downtown Omaha earlier this month.

Police said Wednesday that toxicology results show 44-year-old Steven L. Peterson died from cyanide poisoning.

Peterson was found unconscious outside his car only blocks from where 51-year-old Douglas Plack was shot and killed on July 12. Peterson died later.

Court documents revealed that Peterson had photos of Plack and some other men in his pockets on the day of the shooting.

Plack, 51, was an Army Corps of Engineers supervisor. During a corps staff reduction in 1999, Peterson lost his corps job. His department boss had reported to Plack.

Court documents also detailed items found in Peterson’s car, including three handguns and some ammunition, some knives, packing tape, a pair of handcuffs, a U.S. marshal’s badge, binoculars and a set of lock picks.

At Peterson’s home in Ralston, police found three more handguns, five rifles, four shotguns, some ammunition and two gas masks.

Officers also found a notebook that contained writings about murder and suicide and copies of Peterson’s juvenile court record and other court documents.

Peterson was arrested in 1993 on suspicion of making terroristic threats, using or carrying a concealed weapon to commit a felony and assault in the second degree.

The charges were all dropped.

Peterson had two drunken-driving convictions in his past.