An Adelaide teenager has made a shock courtroom confession admitting he placed a wire trap across a popular southern suburbs bike path.

Levi Young-Henderson handed himself in to Christies Beach police station after officers posted a photo of the suspect online.

Police described the Norlunga teen’s crime as “dangerous” and “stupid”.

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The 19-year-old refuses to explain what motivated him to lay the wire trap for unsuspecting cyclists using the purpose-built bike way.

Four cyclists were thrown from their bikes and badly injured after hitting the wire that was deliberately strung across the busy bike path, alongside the southern expressway.

Upon handing himself in, police confiscated his phone and discovered he had filmed the wire and posted an emoji of a devil and the words “I’m so evil” underneath.

Young-Henderson pleaded guilty to four counts of committing acts likely to cause harm and two of property damage to the bikes.

His lawyer requested a long adjournment to gather psychological reports.

The case returns to court in October.