There is some uncertainty among lawyers as to whether exhibits should be entered in evidence or entered into evidence. According to the Cornell Law Review, in the 1990s, the nine Supreme Court justices were split 6-3, in favor of ‘into’. Steven Lubet, Into Evidence, 81 Cornell L. Rev. 154, 158-59 (1995), available at https://scholarship.law.cornell.edu/clr/vol81/iss1/4/ . However, the article quotes the director of Harvard’s trial advocacy program as saying, "Evidence is not a place into which something goes or is placed. It is a status or a state of being. A thing is either 'in evidence' or 'not in evidence'; it is not 'into evidence' or 'out of evidence."' Id. at 154, quoting Peter L. Murray, Basic Trial Advocacy 14, n.1 (1995). This makes sense to me.
Into should be used when a space is entered (“The happy family went into their new home.”); interest is expressed in something (“Michael is really into cite checking.”); or to describe change (“The home’s master bedroom was divided into three new rooms.”)
A search of both federal and state case law in Google Scholar returns 482,000 hits for the phrase, "into evidence", and 518,000 results for "in evidence". However, since 2000, there have been 210 decisions of the Supreme Court of the United States using, "into evidence", and 142 decisions using "in evidence".