Some 1,700 police officers and support staff searched police online files for information about the rape and murder of 17-year-old Lisa on the outskirts of Amsterdam last year, justice minister David van Weel has told MPs.

Most of them had “no need” to look at the information, the minister said, adding that an investigation is under way. The inquiry was launched after it emerged that a large number of people had accessed the documents.

“It is unacceptable that this has happened” for both the relatives and for the integrity of police systems, he said. “Police officers are only allowed to access the information systems if this is necessary for them to do their jobs,” he said in the briefing.

All the officers involved will be invited to a meeting with their superior and asked to explain why they looked up the Lisa case. If access was justified, they have no cause for concern, the minister said.

The police, who have issued an apology to Lisa’s relatives, are planning to introduce new security checks to prevent files being read without good reason.

The Dutch privacy watchdog AP has also been informed about the illegal access because it can technically be considered a data leak, broadcaster RTL said.

Last month, the man charged with murdering the teenager and with the rape and attempted rape of two other women in Amsterdam last August confessed to all three crimes.

The man, known as Christ Jude, is accused of killing 17-year-old Lisa as she cycled home on August 20, raping a woman on the Weesperzijde in Amsterdam on August 15, and attempting to rape another woman five days earlier.

Lisa’s murder led to countrywide protests, vigils, silent marches and a “We Claim the Night” crowd-funding campaign that raised some €500,000 in three days before it was shut down.