Grammar fix

serious crime

major crime

A crime that is very severe or dangerous, such as murder, robbery, or assault, and usually has strong punishments.

collocationB1common

Hear it in context

Notice where the phrase sounds natural.

The police are investigating a serious crime that happened downtown last night.law
In my opinion, people who commit serious crimes should receive strict punishments to protect society.IELTS speaking

Pattern: serious crime (noun phrase); commit a serious crime; be charged with a serious crime

WrongMurder is a seriously crime.

RightMurder is a serious crime.

'Serious' (adjective) + crime; 'seriously' is the adverb.

Patternserious crime (noun phrase); commit a serious crime; be charged with a serious crime

Choose the version that sounds natural in speech.

Stiff He was convicted of a grave criminal offence.

Natural He was convicted of a serious crime.

'A grave criminal offence' is courtroom-formal; 'serious crime' is the everyday pairing.

Words that usually travel with it.

a serious crime
a serious crimecommit a serious crimeserious offencea violent crime

Contrast with 'minor crime', which refers to less harmful or less serious illegal acts.