noun
criminal nature; criminality
Used to describe whether an incident has the nature of a crime or is likely to be a criminal case. Often appears in news reports and police statements.
警察は事件性があるとみて捜査を始めた。
The police began an investigation, suspecting criminal involvement.
遺体に事件性は認められなかった。
No signs of foul play were found on the body.
Compound of 事件 (incident, case) and 性 (nature, -ity). The exact historical derivation is uncertain, but the word follows a common pattern for forming abstract nouns.