A man has been arrested on suspicion of attempted murder after a 50-year-old was shot in the face.
The victim remains in a critical condition in hospital after the attack in a flat in Old Swan, Liverpool, on Monday, Merseyside Police said.
A 25-year-old from Liverpool has been arrested in connection with the shooting and is being held for questioning, the force added.
Det Ch Insp Jason Pye appealed for any witnesses to come forward.
At about 16:30 GMT on Monday a man is reported to have entered the flat on Haslingden Close and opened fire at the 50-year-old, who was airlifted to hospital with a serious gunshot wound.
Det Ch Insp Pye said police had been "relentless" in their pursuit of the person responsible, and had arrested the 25-year-old on suspicion of attempted murder.
"We understand the fear incidents like this bring to those who live nearby, and I'd like to reassure residents that we will leave no stone unturned when targeting those who are prepared to use firearms", he said.