Police in England and Wales are taking "excessive" amounts of personal data from smartphones during investigations, warned the UK data watchdog.
Taking too much data can deter people from reporting the crime or assisting the police, information commissioner Elizabeth Denham said.
His report on police mobile data mining (MPE) calls for a "code of legal conduct" for the police.
An investigation into MPE continues in Scotland and Northern Ireland.
"Penetrative insights"
In some cases, the police request data from a witness or victim's smartphone, not just from the suspects' devices.
The Office of the Information Commissioner (ICO) began its investigations following concerns expressed by police forces inconsistently in the way they collected data and many adopted "an excessively broad approach to data extraction ".
The report says that cell phones "reveal the patterns of our daily personal and professional lives and allow insight into our actions, behaviors, beliefs and mood."
Taking the data without "significant engagement" with witnesses and crime victims "risks deterring citizens from reporting the crime," said Denham.
Investigation of rape
Campaign group Big Brother Watch said the report confirmed its "long-term view ... the police default approach to requests for searches on digital strips of crime victims is illegal, harmful and must end" .
The group released its report on mobile data collection in rape investigations.
His research suggested that police investigations were stopped when the alleged victims refused to hand over their mobile data.
The group made requests for freedom of information to 22 police forces in England and Wales.
"Dangerous approach"
The agents were found to have requested data on the complainant's cell phone in 84 cases of sexual assault.
And each of the 14 of those in which the complainant had refused had then been abandoned by the police.
"People who report sexual offenses want to provide relevant evidence, but are regularly informed that they have to undergo a full phone draw, give up social media accounts and often more data," said Big Brother Watch.
"This is an incredibly dangerous approach."
