Problem Question

How do you answer the following problem question?
Lucas and Paul had been in the town centre drinking and decided to look around the shops. They were in Sneaker World when they noticed Francis buy two pairs of limited-edition Nike Jordan’s. Lucas and Paul were jealous, they could not afford the trainers so decided to follow Francis with the aim of stealing them from him. Francis walked away from the town centre, and when Paul and Lucas could not see anyone nearby, they grabbed Francis from behind. Paul snatched the bag containing the trainers and Francis responded by head butting Paul, breaking his nose.
Lucas pulled out a knife and stabbed Francis to the arm twice, allowing him and Paul to get away with the trainers. Francis, after stopping the bleeding from his arm started to run after them. He caught up with Lucas and Paul on a foot bridge that crosses a fast-flowing river. Lucas and Paul grabbed Francis again and decided to throw him into the river so that they could escape. Just before they threw Francis into the river, Francis shouted, “I can’t swim”.
Pam witnessed Francis land in the river and phoned 999 and the emergency services were quickly at the scene. Francis was dragged out of the river and taken to hospital. Unfortunately, the doctors did not realise how much water Francis had swallowed and by the time they had devised a treatment plan, Francis had died.
When Lucas heard about Francis’s death, he started to panic and went to talk with Paul. Paul said that they must call the police to confess and took his mobile phone out of his pocket. Lucas shouted at him ‘don’t you ******* dare, or I will kill you’. Paul then started to cry and screamed that they were going to rot in jail. To calm Paul down, Lucas prepared a syringe of heroin, and with Paul’s consent injected him with the heroin. Paul soon started to feel unwell and quickly lost consciousness, hitting his head on a table as he fell to the floor. Lucas, on seeing Paul lying on the floor unconscious decided to run away.
Paul was discovered by mum a few hours later and was taken to hospital. Paul responded well to the initial treatment but needed an urgent operation due to internal bleeding on his brain. Paul refused the operation, and he died a few days later. The doctor told Paul that he would survive if he let him operate.
Advise on the criminal liability of Lucas and Paul.