Green card holder marrying a US Citizen

Not me but I know someone who had a green card for 3ish years before they married a girl who was a US citizen. I know the guys family convinced the girls family that the son in law had just came to America (I don’t remember if this was part of some scheme but I’m not sure why someone would want to lie about just immigrating to America when they’ve been here for 3 years). But I was wondering is it faster for green card holders to become citizens if they marry someone who is a US Citizen, or do they still wait the 5 years?