Detectives are investigating links between the murder of a retired teacher, the stabbing of a nine-year-old boy and an incident in which a girl of eight was chased through a garden.
Louisa Denby, 84, was found with multiple stab wounds at her home in Prospect Mount, Shipley, West Yorkshire, shortly before midnight on Monday.
Police believe her murder is connected to an attack on a schoolboy in a skate park at 4.40pm the same day and are questioning a 26-year-old man on suspicion of murder and attempted murder, West Yorkshire Police said.
The boy was stabbed in what witnesses described as an apparently random attack, and was left covered in blood.
He was airlifted to hospital from the Carnegie skate park with chest and arm injuries, and was last night in a stable condition.
The incident involving the girl happened about 10 minutes later in nearby Prospect Grove. Police said she was chased through her garden before taking refuge in her house.
The man ran off when she screamed and detectives said she was not hurt and did not mention seeing a weapon.
Det Supt Lisa Griffin, who is leading the police inquiry, said yesterday: "The nine-year-old boy was out playing and was returning home for a drink when he was approached by the male suspect and, with no prior warning and for no reason known to us at this time, he was attacked with a knife - a single stab wound causing him injuries to his chest and his arm."
She added: "It's my belief at this time that the three incidents are linked."
The 26-year-old man was arrested at 4.10am yesterday after being spotted by a member of the public in Bradford, police said.
A second 26-year-old man has also been arrested in connection with Mrs Denby's murder, while three men aged 18, 24 and 29 were held over the incident in the skate park. The 24-year-old was later released without charge.
Police said they are not looking for anyone else in connection with the stabbing or the murder.
Griffin confirmed a knife was recovered, and police and forensics officers were working on 10 different scenes in the area.
Mrs Denby was described by neighbours as a "lovely lady" and "everybody's grandma".
Lisa Lacey, who said her 18-year-old son Eli saw the boy being stabbed and chased his attacker, said she was distraught when she found out her neighbour had died.
She said: ""I just broke down. I was sobbing... sobbing.
"She was everyone's grandma. She was a lovely lady - just the type of person you want for your nana.
"She didn't harm anyone. She was always in her garden, she loved it.
"For something to happen on your own doorstep like this, it's a nightmare. You just don't believe it."