1. Soviet-Finnish war, Tragedy at Lemetti. Guide-book of the area. Petrozavodsk, Karelia, 1999 [Karelian/Russian]. My initial source.
2. M. Jokipii. Finland on the way to war. Petrozavodsk, Karelia. 1999. Some short descriptions about combats in the area only.
3. B. Sokolov. "Mysteries of Winter war". Moscow, Veche. 2000. Some info from here was found by Art/Juha already, see my translation above.
4. V. Taras, ed. "Soviet-Finnish war 1939-1940". Minsk, Harvest. 2000. Still not translated the relevant pages, but I took some data about Soviet losses from this book [it is mentioned, that data are from TsAMO = Central Archive of Ministry of Defense].
Several Internet resources can be found easily - type Lemetti 1939, 1940 or Ëåìåòòè 1939, 1940 on Russian.
As for NKVD archives - most probably, they were initial source of the info [Bair should know better]. NKVD soldiers entered the territory after Peace Treaty at first, of course. As for NKVD reports - if they were secret reports to NKVD command [I don't know what kind of reports are they], they should be very truthful [I don't recommend to read secret reports of NKVD to people with neural problems because of very detailed descriptions of enemy and own crimes as usual daily things - I read 2-3 of them as translation variants], propaganda reports were written mainly by political departments and commissars, that was their job, not NKVD.
I don't know as I didn't investigate this question in details. I read just mentions about such cases in the literature about war in Karelia in 1939-1944, eye-witnesses Zlatkin and Kattonen answered only shortly on the huge amount of questions during interview [need to find the lost link and provide you with it], they didn't mention details if not specially asked by journalist - Zlatkin mentioned [as eye-witness] ~150 doctors, nurses and wounded soldiers who were knifed by Finnish skiers in a hospital, and mentioned several more cases about which he heard from ski scouts of his unit.JT wrote:
Hospitals - Petrovski Jam ? ( a distant relative of mine was there ) Where there others?
I don't have time to investigate such sad subject as Finnish war crimes in Karelia [several sites describes Finnish Petrozavodsk POW camps in details, and their occupation regime in Karelia], but here is one link from the newspaper "Karelia" about billeting of Finnish units near Moscow and their exceptional cruelty to civil population [according to village civil eye-witnesses] - http://www.gov.karelia.ru/Karelia/1558/21.html [as I never heard about Finns near Moscow, try to translate this some day, but I understand that the author of the link discussed the possibilities of such facts, not confirmed them for sure, could some civilians confused Finns with Germans?].
Regards, BP