The author Irvine Welsh has led tributes to the Trainspotting 2 actor Bradley Welsh, who was shot dead on his doorstep in Edinburgh while his wife and child were at home.

Police Scotland confirmed on Thursday that the killing was being treated as murder and reassured the public that, while shootings remain extremely rare in the Scottish capital, considerable resources would be dedicated to the inquiry.

The 42-year-old former boxing champion and reformed football hooligan was killed in the West End of the city on Wednesday.

Police said Welsh had been killed on the doorstep of his home in Chester Street when his wife and young daughter were inside. He was killed by a shot to the head as he walked down the stairs to his flat.

A neighbour who heard the gunshot found Welsh fatally wounded outside his flat, but it was only once police arrived that his family learned of his death.

Det Supt Allan Burton, from the major investigation team, said: “We have a lady who’s lost a partner, a child who’s lost a dad, a family who have lost a son and brother.”

Irvine Welsh, the Trainspotting author, said on Twitter that his “heart is broken”, adding: “Goodbye my amazing and beautiful friend. Thanks for making me a better person and helping me to see the world in a kinder and wiser way.”

A forensics team searches for clues near floral tributes left for Bradley Welsh at the scene of the shooting in Edinburgh. Photograph: Jane Barlow/PA

Bradley Welsh, who was born in Moredun, a district of Edinburgh, starred alongside Ewan McGregor, Ewen Bremner, Jonny Lee Miller and Robert Carlyle in T2 Trainspotting, playing the role of gangland figure Mr Doyle.

Detectives said they believed Welsh had been shot in a targeted attack by a man who fled the scene on foot.

In a plea for witnesses, Burton called for people who “have got any information, or have heard any rumours or speculation, or know someone who’s acting differently after the events of last night and are suspicious of this individual – please come forward”.

Burton said: “Murders remain extremely rare in the capital, and such incidents where a firearm is used are even more uncommon. However, we wish to reassure the public that considerable resources are being dedicated to this inquiry and we are treating this matter with the utmost seriousness.”

The former British ABA lightweight boxing champion and Hibs supporter was involved in charity projects in Edinburgh, including helping young people stay away from crime through his Holyrood Boxing Gym. He also appeared in Danny Dyer’s Deadliest Men and The Real Football Factories, describing himself as a “born leader”.

Tributes were paid on social media, with one woman posting a picture of herself and friends alongside Welsh in a boxing ring: “You to me are treasure, you to me are dear. Our coach, our motivator but most importantly our friend, Brad Welsh.”

One man described Welsh as a “huge character” in Edinburgh. “Devastating news about Brad Welsh tonight, a huge character in Scottish amateur boxing and the Hibernian supporter and someone who contributed a great deal to society through his charitable work and boxing gym. RIP.”

People view floral tributes on Chester Street in Edinburgh. Photograph: Jane Barlow/PA

On Thursday dozens of forensics officers were searching Chester Street and neighbouring roads within the large police cordon.

Burton added: “We’ll be looking to see if anything has been dropped, discarded, someone’s been standing by waiting for Mr Welsh to return. Any cigarette butts, cans, etc could indicate the presence of any individual.”

Bunches of flowers, cards, teddy bears and football scarves in the colours of Hibernian Football Club were laid at the edge of the police cordon by friends and family.