The sanctions are usually very light. Sanctions depends on institutions' willingness to reprimand the perpetrators.
In the case where this person is copying earlier conference contributions and claiming them as their own, it's a clear case of plagiarism. If the conference contribution is archived in a way, notifying the journal will result in the retraction of the paper. This will hurt the plagiarist's reputation possibly at the cost of a prospective employment opportunity.
In the case where a person "steals work of two graduate students, passes it off as his own" in the absence of publications that shows the work is effectively the students' journals are faced with a "someone's word against someone else's" situation. Often journals defer the responsibility of investigating to the author's institution. This can be a lengthy process with disappointing outcomes for the students.
All of this is off course highly unethical and all reputable journals will want to retract papers if they learn they weren't written by the alleged authors. But it's not illegal per se and "sanctions" range from nothing (the most frequent case) to a few years of publication ban, and in extreme cases: getting fired.
Some reading on the topic:
Arizona prof plagiarizes student’s thesis, gets reprimanded, but keeps her job
Heads up: “Borrowing” your student’s work will earn you a partial retraction — and a five-year publishing ban
If besides being interested in "what are the sanctions" you are wondering what you can do about it, my recommendation would be:
- explore all internal reporting routes: report the behavior to this person's adviser, or to the dean.
- If all fail (i.e. if they do not ask for the authorship record to be straighten) contact the journal's editors.
In all cases, be prepared to substantiate your claims. You mentioned you have lab notebook, or even conference publications to show that the material is not original. That is good. Don't expect a harsh punishment but at least the papers should be retracted.
(This answer has been adapted to the latest changes in the question)