The man was armed and considered dangerous. Police arrested him early on Tuesday morning, near Feldkirchen. His getaway car, a white Suzuki Splash, was found on Monday evening, not far from his parents' house.
The manhunt had focussed on the village of St Ulrich, where roads were blocked off and a nearby forest was searched overnight with thermal imaging cameras and a helicopter.
Erwin P is believed to have shot 53-year-old Franz W three times in the face as he sat in his parked BMW in Mageregg Castle car park on Sunday afternoon.
The dead man was in a relationship with Erwin P’s ex-girlfriend, who was reported to have been sitting in the car beside Franz and witnessed the murder.
Franz W has two daughters, aged 17 and 18. Police said he died instantly.