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The unemployed apparel designer who killed a former coworker near the Empire State Building on Friday morning left his Manhattan apartment intending never to return, according to a police source with knowledge of the investigation.

The police source told CNN that when Jeffrey Johnson closed his door, he left the keys behind for the landlord before heading off to shoot Steven Ercolino.

The landlord was surprised, the source said, because Johnson was scheduled to move out a week later on August 31 in anticipation of apartment renovations.

Johnson apparently told the superintendent earlier in the week he had found a new place to live, had placed his cats with friends and that, "Things would be resolved by Friday."

On that day, Johnson, 58, returned to Hazan Import Corp., the company where he'd been laid off about a year earlier due to downsizing.

Police say he waited outside for Ercolino, a 41-year-old sales executive whom he blamed for losing his job. He shot Ercolino five times in the head, according to the New York City medical examiner.

Police are searching through files on Johnson's computer found in his apartment, along with several books on shooting such as "Sniper: The Techniques and Equipment of the Deadly Marksman," according to the police source.