Maybe... but I've recently learned that "prison days" don't equal "real" days. Here's more info:
http://www.iowapublicdefender.com/outlines/FUN WITH NUMBERS.pdf. I hope this is an OK link - I found similar info other places but this one was Iowa specific, so I went with it.
A few snippets for the math inclined, BBM part for the non-math inclined.
Basically, every 166 days discharges a year. Got a 5 year sentence? 5 x .4545 = 2.2725 years. .2725 x 365 = 99 days. Discharge is in 2 years and 99 days. Got a 6 year sentence? Add 166 days. For a 7 year sentence, add 332 days. An 8 year sentence would discharge in anadditional 1 year and 133 days. A 9 year sentence adds 1 year and 299 days to the five year
sentence.
BUT... there's also this:
1. Earned Time Credit is the 1.2 days credit inmates receive for every day they serve in custody. They get this for prison days, jail days served prior to going to prison, mental health treatment days (court ordered), and half-way house time.
I'm not sure if the mental health treatment applies here but I know Misty was in a half-way house for awhile as reported in the early stories. I still think serving only 5 months on a 4 year sentence sounds low, but this explains part of why it was likely much less actual time in prison. She might've done some of her time in jail before that too, but only the prison time is being reported.
Why they do this I have no idea, it's maddening! The only thing I can think of is to make victims/the public feel vindicated when someone gets a long sentence like 10 years. What they don't realize or later get really upset about is if the prisoner behaves, s/he will get out MUCH sooner. If I'm reading this right it sounds like for certain violent crimes the convicted person has to serve at least 70% of their sentence. For non-violent it sounds like the minimum is 1/3 of their sentence. Maybe it's also used as an incentive for good behavior from the prisoners.
In California, I have heard antecdotally, probably because our prisons are so over-crowded, that for non-violent crimes 1 "prison day" can equal 3 "real" days. And lawyers try to keep their clients tied up in "jail" for as long as possible because in most cases the jails are a lot less crowded than the prisons. Again antecdotally (but from multiple sources) say you've got 4 years in California state prison, and the case takes 6 months while you're in "jail." Multiply by 3 and voila, you already served 18 months of your sentence. So you go to "prison" with 2.5 years left, which is really only ~1 year (around 10 months I think? Math is not my strong suit.
Add a halfway house and the early releases for non-violent offenders, and 5 months on a 4 year sentence is entirely possible.
I'm not sure how that works between Federal vs. State prison though, or which type of prison we're talking about in the above quote.
For those inclined to learn more I found this handy calculator:
http://www.prisoncalc.com/.
And I know this does nothing to help bring the girls home.
but it might help with figuring out a motive for the crime.