The number of juveniles investigated over crimes in the first half of the year dropped below 20,000 for the first time on record, due mainly to a decline in petty crime, police data showed Thursday.

The number of juveniles involved in serious offenses also declined to 275, down 58. Of those, robbery, arson and rape decreased, but murder investigations were up by four to 26, the data showed.

Between January and June a total of 19,409 juveniles were suspects nationwide, down 3,601, or 15.6 percent year-on-year, to mark the lowest level since police began taking records on a half-yearly basis in 1979, according to the National Police Agency report on juvenile crime.

But the number of those involved in emergency scams and other forms of bank transfer fraud increased from 164 to 183 — a record high.

The police data showed the number of juvenile suspects in shoplifting, bicycle theft and other delinquencies fell to 11,787, down 2,414 or 17 percent.

An NPA official said the decline in minor offenses was a "major factor" in the overall drop in juvenile crime.

The number of repeat offenders declined by 1,046 to 7,179, but the recidivism rate was up 1.3 percentage points to 37 percent, marking the sixth consecutive year of a first-half increase.

The number of criminal cases stemming from bullying was down 50 at 99, with 180 minors investigated or taken into police custody, down 79.