Gianluca Ros, 48, waited in the stairwell of the apartment building, wearing the coat and a blond wig, as his ex-boyfriend returned from a holiday in the Canary Islands with his new boyfriend, Jørn Husby, on 15 November last year.
He then attacked Husby (40) with an axe, killing him, and then knifed down his 36-year-old ex, who was brought to hospital with life threatening injuries.
The 36-year-old told the court that he had been previously romantically involved with Ros, and that he had become fearful after he began making angry phone calls to him while he was on holiday with Husby.
"Since he was in disguise, I think he was planning the act," he said, according to Norway's public broadcaster NRK. "I saw a lady in a coat, and I thought that maybe she was lost. Suddenly, she attacked."
In court on Wednesday, Ros maintained that he did not consider himself to have split up from the 36-year-old, so his lover's decision to go on holiday with someone else had sent him into a rage.