"I can't see how Lausii didn't score that try," Larkham said.
"There is no other possible answer to what happened there. It was clearly a try, to everyone who saw it.
"It is really disappointing that a game comes down to that. We should be in the semi-finals right now.
"I give credit where it is due and I thought the Highlanders played really good football but I think we deserved that win tonight. To go out of the competition with (departing) guys... missing out on an opportunity to win a Super Rugby title, it is really disappointing."
Brumbies captain Stephen Moore said Taliauli was positive in the sheds post-match he had grounded the ball.
Larkham was also frustrated that several dominant Brumbies scrums near the end weren't rewarded with penalties.
"The boys did everything right, it was a seesawing battle," Larkham said.
"But we got to the point where we deserved to win that game. It is incredibly frustrating now to know we lost it that way."
The Brumbies failed to score a try at home for the first time since last year's semi-final defeat at home to the Hurricanes, and it served to be very flat end to the ACT careers of Reds-bound Moore and overseas-bound centre Matt Toomua and wing Joe Tomane.
"It's disappointing obviously," Moore said.
"We had or chances there at the end but couldn't get the ball over the line.
"We defended well but couldn't take our chances in the second half.
It was a tight game but they always come down to those few opportunities. They took them and we didn't."
The Brumbies missed their moment at the end but the Highlanders snatched theirs when a Lima Sopoaga intercept in the second half set up Liam Squire for a crucial try.
Coming after a Waisake Naholo try in the first half, the Kiwis were then able to defend their way home with incredible grit.
Watched by just 8559 in the unusual 6pm kick-off slot, the Brumbies looked up for the fight and led for much of the first half.
They only trailed 10-9 at the break but their line out malfunctioned as an attacking platform in the second half and it hurt them badly.
Several promising raids into the Highlanders territory came to nothing due to line out losses.
It ensured the exit of the last Australian team from Super Rugby this season.
Moore said he would fondly remember his time in Canberra after eight seasons with the Brumbies.
"It hits you a bit at the end there that that's it. I am very proud to have been a part of this proud club and hopefully I have made a contribution in a positive way," he said.
Larkham delivered huge praise to his departing captain, saying he had delivered an unrelenting drive for improvement at the club.
"He is the most passionate leader I have been lucky enough to either play or coach with," Larkham, who played under John Eales and George Gregan, said.
