Police are urging parents to monitor their teenagers' mobile video phones, following a craze of filming crimes being committed.
Deleted footage can be traced by police
Merseyside Police said they had found footage including dog fights, loaded guns and speeding cars being passed around by mainly teenage phone users.
A senior officer said that police had the power to seize phones and can even trace deleted videos.
The recorded incidents are believed to have taken place in Liverpool.
They included clips of loaded guns being brandished and cars and motorbikes being driven recklessly.
Ch Supt Andy Ward, of Merseyside Police, said that it was not only those doing the filming who were at risk of prosecution.
"We will be investigating both the making and distribution of the footage and have the power to seize phones," he said.
"We must also warn people that deleting the footage is not enough - it is still traceable."
He said he was concerned that children may be tempted to join the craze and put their lives at risk.
He added: "I would say to parents 'Are you aware of where your children are and what they are doing?'.
"I'm talking about the 14 to 19 age group here.
"If you get the opportunity, have a look at your sons' or daughters' phones and see what is on it, because some of these children may just be on the periphery and thinking of getting involved in this sort of behaviour because it is glamorised.
"The last thing I want to happen is for me to have to go around to one of their houses tonight and ask them to come to the mortuary to identify their son or daughter."