I just read Brian D. Rubendall's review and have to write a quick counter-review. I'm in the middle of a project to re-read the entire John Marshall Tanner series, started with the later ones trying to find a particular line of JMT's and then began at the beginning, and this the peak so far. And I've recently read both of the ones recommended by the previous reviewer as alternates. "Past Tense" is also excellent, but depends too much on the series' past history, and is too much a turning point in the series, to really recommend as a starting point. I would, however, recommend the neophyte begin with "Grave Errors," not because it is superior to "State's Evidence" (this is #3 in the series) but just because one really should see the development of the lead character, the cast, and the author in proper order, in spite of the writing being a bit ragged, stretching a bit too much for effect, in the freshman venture.
Admittedly the plot in "State's Evidence" is complex, and there were one or two points where I had to pause and think "now wait a minute, just who is this again?" as clues lead us madcap from one setting or character to another. But as Tanner is led from clue to hint to revelation, it's not really that hard to follow along, although we must remain as bemused and puzzled as the PI himself, since everybody ... everybody ... is lying to him. I felt it all fell together rather well in the end. Indeed, the revelations near the end made some of the more bizarre elements from early on make sense, fall into place.
What really makes the book ... and the series ... though is Greenleaf's writing, Tanner's snappy, cynical first person narrative. In "Grave Errors" the voice was a little too obviously the author's, not the character's, but by "State's Evidence" there seems to be no difference between the two. Sometimes it is sharp and precise, with a twist -- "Tolson would be doing what all DA's do, deciding who to prosecute and who not to, what charge to file, what plea to accept, ..., dispensing more justice in a day than anyone else in the county would dish out in a month." (p. 6) And Greenleaf/Tanner's liberal inclinations (see also the penultimate novel, "Strawberry Sunday") are beginning to blossom, e.g. "She shook her head wearily, a classic victim of poverty's cycle, a descendant of the proud but hapless occupants of Walker Evans's photos and Erskine caldwell's books." (p. 133)
There is a large cast of memorable characters, but outstanding are the two boys central to the plot, fully realized, realistic and intriguingly contrasting, one sweetly resilient the other maybe a monster in the making.
I'm not sure what the previosu reviewer would consider "the best of the genre" to which he contrasts Greenleaf's books, but I don't think I've read better. He's certainly up there with Matt Scudder, and has a serious core lacking in the Spenser books. But hey, who really cares which one is a smidgen better than the other ... we've got them all, which is all to the good.