Maura states that the runic alphabet "...predates Latin." She is wrong. The earliest runic inscriptions appeared around 300 CE, more than 1,000 years after the founding of the city of Rome.
Iceland is not a part of Scandinavia. Scandinavia consists of Norway, Denmark and Sweden. Iceland is considered a Nordic country, together with those three and Finland.
The game name of the killer is Undimaor which is not pronounced untermater as all the characters said it.
Both Maura and Jane list either dead people or fictional characters as mentors. The definition of mentor is an experienced and trusted adviser, meaning a living real life person who interacts with the person being mentored. They were talking about role models or inspirational people, not mentors.
Testing hair will not reveal what a person ate as Maura claimed. Once food is digested only the nutrients are absorbed into the body, but there is no way to determine what the original food was.
The girl said she needed the hundred dollars to buy a textbook. High school students do not buy textbooks, they are provided by the school. She is definitely in high school because she says she taking A.P. Biology which is a college level course taught in high school to prepare students to take the A.P. test. Also, if she were lying either Jane or Maura would know it, so it is definitely an error in the plot.
The runic inscription on the harpoon's head is not Old Norse, but rather English using Runic characters. It does not spell "Óláfr hinn beinlausi" (as the name would be in Old Norse), but rather "Olaf the Boneless".