Several agencies may hire you right out of college.
Ok, that being said.. it is not the norm. Most that are hired right after (or shortly after) college also bring something to the table. Remember, that it is rather easy to be qualified for a fed criminal investigator job (I assuming these are the fed jobs to which you are referring). However, to get hired, one need to meet the "most competitive" category. Most make this through a combination of college, military and/or experience. LE experience is not necessary, but you will need to bring something to the table. 
Your best bet is to apply to the fed jobs you want and go on with your life as if those apps are not even out there. It is a long process and you cannot put your life on hold in the meantime. Always do things to make yourself more marketable, whether it is getting hired by a PD, certifications, a second language, community service, etc.
We bring evil things to evil people, kicking in a door near you!
."In theory, there is no difference between theory and practice. But,
in practice, there is."
- Jan L.A. van de Snepscheut
"The difference between 'involvement' and 'commitment' is like
an eggs-and-ham breakfast: the chicken was 'involved' - the pig
was'committed'."
-unknown
Working on a PhD in CQB one doorway at a time.
When the wolf attacks, he will find not all who run with the flock are sheep!