(;GM[1]FF[4]CA[UTF-8]AP[CGoban:3]ST[2]
RU[Japanese]SZ[19]KM[6.50]TM[1800]OT[5x30 byo-yomi]
PB[alleged cheater]C[KataGo terms:

Blue = KataGo’s first move candidate
Green = A move candidate almost as good as the blue move
Yellow = A valid move candidate
Red = A move considered by KataGo, but probably not a very good one

My terms:

Obvious = ‘Most players would play here’ or ‘only move’
Common = ‘It’s not so hard to think of this move’
Conceivable = Not your usual first idea, but still a common enough move
Surprising = ...well, surprising.]RE[B+Resign]
;B[pd]BL[1788.123]C[Common; blue]
;W[dp]WL[1795.902]
;B[pp]BL[1784.861]C[Common; blue]
;W[dd]WL[1794.365]
;B[fc]BL[1780.431]C[Common; blue]
;W[cf]WL[1791.693]
;B[cq]BL[1771.843]C[Common; blue]
;W[cp]WL[1767.216]
;B[dq]BL[1766.75]C[Obvious; blue]
;W[ep]WL[1763.552]
;B[fr]BL[1758.945]C[Common; blue]
;W[qq]WL[1751.353]
;B[pq]BL[1698.708]C[Common; blue]
;W[qp]WL[1749.357]
;B[qn]BL[1696.764]C[Common; blue]
;W[qo]WL[1744.879]
;B[po]BL[1694.105]C[Obvious; blue]
;W[rn]WL[1743.614]
;B[dl]BL[1683.189]C[Conceivable; red
No winrate drop, i.e., just as good as the blue move.]
;W[qc]WL[1708.62]
;B[pc]BL[1671.603]C[Common; blue]
;W[qd]WL[1707.397]
;B[pe]BL[1669.506]C[Common; blue]
;W[rf]WL[1697.135]
;B[gq]BL[1641.058]C[Common; blue]
;W[cj]WL[1649.128]
;B[go]BL[1609.077]C[Common; green]
;W[fn]WL[1582.366]
;B[fo]BL[1585.619]C[Conceivable; blue]
;W[dn]WL[1567.397]
;B[dj]BL[1575.987]C[Conceivable; blue]
;W[ck]WL[1556.357]
;B[cl]BL[1500.786]C[Common; blue]
;W[fl]WL[1522.476]
;B[dk]BL[1488.649]C[Obvious; blue]
;W[er]WL[1463.57]
;B[eq]BL[1477.28]C[Obvious; blue]
;W[fp]WL[1462.36]
;B[gp]BL[1428.821]C[Obvious; blue]
;W[bn]WL[1423.136]
;B[ci]BL[1414.859]C[Common; blue]
;W[bl]WL[1410.587]
;B[bi]BL[1409.079]C[Common; blue]
;W[bj]WL[1408.581]
;B[eh]BL[1397.948]LB[aj:A]C[Surprising; yellow
Who wouldn't play the obvious atari of A?]
;W[gn]WL[1396.588]
;B[hn]BL[1367.899]C[Common; yellow]
;W[hl]WL[1387.983]
;B[hm]BL[1360.437]C[Common; yellow]
;W[gl]WL[1364.297]
;B[qg]BL[1289.626]C[Common; uncoloured
A relatively big mistake according to KataGo, losing two points.]
;W[rg]WL[1351.346]
;B[qh]BL[1286.89]C[Common; uncoloured
A relatively big mistake according to KataGo, losing two points.]
;W[qm]WL[1340.027]
;B[pn]BL[1283.311]C[Obvious; blue]
;W[qr]WL[1338.945]
;B[pr]BL[1264.81]C[Common; red
A small mistake, losing about 0.7 points.]
;W[jn]WL[1208.763]
;B[jm]BL[1142.901]C[Common; red]
;W[km]WL[1180.317]
;B[kn]BL[1096.344]LB[im:A]C[Surprising; red
A big mistake according to KataGo, losing three points.
I cannot think of a strong human player who would play here, as the mistake is too obvious – white will just play A.]
;W[im]WL[1007.688]
;B[jl]BL[1092.453]C[Obvious; blue]
;W[in]WL[1005.492]
;B[ko]BL[1089.744]C[Conceivable; red
A big mistake according to KataGo, losing 2.7 points.]
;W[fq]WL[985.691]
;B[gr]BL[1084.071]C[Common; green]
;W[bq]WL[949.994]
;B[dr]BL[1078.353]C[Common; green]
;W[ec]WL[888.501]
;B[fd]BL[1062.865]C[Obvious; blue]
;W[ff]WL[855.606]
;B[ef]BL[1013.533]C[Common; green]
;W[ee]WL[850.053]
;B[df]BL[1012.142]C[Common; blue]
;W[fe]WL[835.795]
;B[ce]BL[1009.643]C[Common; blue]
;W[de]WL[824.983]
;B[cg]BL[973.944]C[Common; blue]
;W[bf]WL[821.517]
;B[be]BL[971.576]C[Common; blue]
;W[bd]WL[818.912]
;B[bg]BL[965.182]C[Obvious; blue]
;W[jc]WL[783.72]
;B[id]BL[903.82]C[Common; blue]
;W[ic]WL[771.697]
;B[hc]BL[894.815]C[Common; blue]
;W[hb]WL[752.695]
;B[hd]BL[860.532]C[Common; green]
;W[jd]WL[717.062]
;B[gb]BL[831.021]C[Common; blue

The record ends here. Here are some statistics:

Total moves by black: 46

Blue moves: 31
Green moves: 5
Yellow moves: 3
Red moves: 5
Uncoloured moves: 2

Obvious moves: 9
Common moves: 31
Conceivable moves: 4
Surprising moves: 2

Of obvious: all blue
Of common: 20 blue, 5 green, 2 yellow, 2 red, 2 uncoloured
Of conceivable: 2 blue, 2 red
Of surprising: 1 yellow, 1 red

The above data at least suggest an extremely strong human player. No obvious moves were missed, even the surprising moves were among the AI’s consideration, and 67% of the moves hit the blues.

Looking at the content of the game, it is not hard to come up with a plausible story for some of the ‘misses’. From move 51 to 65, Black’s play seems worse on average than the rest of the game. It seems possible that for a moment Black picked their moves by themselves, either being sure that they already had the game in the bag – or possibly in an attempt to make the game look less like an AI’s.

One of the biggest hints in this game is the cut at l6. If we assume that the game was completely played by a human, l6 is inconceivable. L6 is not made by mistaken reading, but by lacking fundamental understanding of the game; however, the rest of Black’s content is top-notch. Although l6 is only a single data point in this game, it makes me strongly suspect that either there were two separate black players, or that the game was not played in good faith.

From this game alone, I would strongly suspect that black is using an AI, but I would still waver if I had to choose whether to convict black or not. However, in this particular case we have three more games by the alleged cheater, all of which are just as suspicious, and we also know that the player was playing as a 5k. With this added evidence, I don’t think there is space left for doubt.])
