offender, criminal 和culprit 都有“罪犯”的意义，但区别如下

(1)Offender指任何违反法律的人，不一定受法律的制裁，还可以表示造成问题的人（或事物）

a juvenile offender (少年犯)、 an old offender (惯犯)；

The authorities often know that sex offenders will attack again when they are released.

当局一般都知道性犯罪者在获释后往往会再次犯案。

The contraceptive pill is the worst offender, but it is not the only drug to deplete the body's vitamin levels.

避孕药的危害最大，但是它并不是唯一一种消耗体内维生素的药物。

(2)criminal指严重犯法的人，理应受到法律的制裁，还可以当做形容词，表示犯罪的，刑法的，罪过的;严重错误的。

如 a war criminal (战犯)、a habitual criminal(惯犯)； 

A group of gunmen attacked a prison and set free nine criminals in Moroto.

一伙持枪歹徒袭击了莫罗托的一所监狱，放走了9名罪犯。

Her husband faces various criminal charges.

她丈夫面临多项犯罪指控。

At 17, he had a criminal record for petty theft.

他17岁就有了小偷小摸的犯罪前科。

Doug was found guilty of criminal assault and sentenced to six months in jail.

道格被判犯有人身攻击罪，监禁6个月。

He said a full-scale dispute involving strikes would be criminal.

他说如果出现罢工等大规模纠纷那将是极不应该的。

(3)culprit则指已被起诉犯下罪行的人。还可以表示引起问题(或不利情势)的事物

All the men were being deported even though the real culprits in the fight have not been identified.

尽管真凶尚未查出，所有参与斗殴的男子均被驱逐出境。

About 10% of Japanese teenagers are overweight. Nutritionists say the main culprit is increasing reliance on Western fast food.

大约10%的日本青少年超重。营养学家指出主要原因是对西式快餐越来越依赖。