This is the link to National Archives Records Administration (aka, where our government keeps all available veteran documents):
http://www.archives.gov/veterans/
Next of kin can ask for and receive all existing records of a veteran's service, and their medals if still available.
The person requesting will need either a Social Security number, or the military service number for 1stSgt Heister. They will also need to know his EXACT place and date of birth and death (many family members do not actually know these things precisely).
If necessary, go here to find his SSN:
http://ssdi.rootsweb.ancestry.com/
When it comes the moment, in filling out their online or hard copy form, to specify what records are requested, it has been found beneficial to use these exact words (not fewer, not more):
“I am seeking all official pages of the official military personnel file and and supplemental pages reflecting service schooling, education, air/sea travel, duty assignments, weapons qualification, special equipment or skill qualifications, awards, medals, decorations and commendations, combat service and injuries and all other military service related entries including medical records and any and all Performance Evaluation Fitness reports.”
They will only provide what is requested. So, if one were to request, for example, "All military service records", NARA would have no clue what was being asked for. Many people make this mistake and are lucky to get a copy of the discharge papers.
It can take some time, and may require more than one request. It may also cost a little money if a hand search must be completed to provide and copy the records.
It is worth the effort, and is really the best way to know what 1stSgt Heister did in the Army. Be mindful, clerical errors are not uncommon.