A 15-year-old boy was distributing food to the homeless hours before his murder, police have revealed.
One week after Jacob Abraham was stabbed behind his home in Waltham Cross, Hertfordshire, officers have released CCTV footage of him shopping for bread on the day he died.
It shows him buying several loaves at 16:40 GMT on 7 December. He was murdered just hours later.
A 14-year-old boy has been arrested on suspicion of his murder.
He has been released while inquiries continue.
The footage shows Jacob buying bread in Iceland on the High Street in Waltham Cross.
He then went home to help his mother make sandwiches before the pair went to their church in Edmonton and distributed the food among homeless people.
The pair arrived back in Waltham Cross just before 20:30 where the teenager received a number of phone calls and went out.
Sometime before 21:30, he was fatally stabbed in a service road that runs behind his home in Hurst Drive.
Police said he attempted to run home but was found collapsed and dying by his 19-year-old brother and pronounced dead at the scene at 22:15, 10 days before his 16th birthday.
Officers said they want to speak to any young people in the area at the time and also anyone who saw a group of teenagers running from the scene.
Det Chief Insp Jerome Kent said: "This poignant footage shows Jacob running an errand for his mother before they both committed an act of kindness in giving sandwiches to the homeless. Just hours later, Jacob had been murdered.
"I strongly believe the clues to why Jacob has been murdered lies within the community of Waltham Cross, and I urge those who have information and have not yet spoken to us to please come forward.
"Help us give Jacob's family the answers they deserve."