Investigators say the attackers had received significant amounts of cash and cryptocurrency from Ukraine
Defending champions Bayern halved Dortmund's lead to three points on Friday with an impressive 3-1 win at Hoffenheim before Dortmund face a tricky away clash at fourth-placed RB Leipzig later Saturday.
Third-placed Gladbach, who are enjoying one of their best seasons, deserved their win at Leverkusen, whose coach Peter Bosz took charge of his first Bundesliga game after replacing Heiko Herrlich last month.
On the first weekend of the Bundesliga after the winter break, Gladbach breached Leverkusen's defence when captain Lars Stindl split the defence with a superb pass before Plea fired home his tenth goal this season eight minutes before the break.
Leverkusen had second-half chances as their Germany teenage international Kai Havertz fired wide, Karim Bellarabi hit the post and Jamaica winger Leon Bailey had a penalty appeal turned down.
Plea, 25, has been a revelation on the road for Gladbach since joining from Nice last July with eight of his league goals so far having been scored away from home.
The away win leaves Gladbach three points behind Bayern and six adrift of Dortmund.
Elsewhere, Eintracht Frankfurt climbed to fifth, a point from the Champions League berths, with a 3-1 win at home to Freiburg as striker Luka Jovic claimed his 13th goal this season to become the league's top-scorer.
A header by Sebastian Haller gave Frankfurt the lead on 34 minutes before the hosts pulled away with two superb goals.
Croatia forward Ante Rebic beat three defenders with a dramatic change of direction, which created space to curl his shot into the goal on 40 minutes.
Jovic, who scored five goals in one league game in October, added Frankfurt's third just before the break before Nils Petersen pulled a goal back from Freiburg in the second half.
Werder Bremen climbed to eighth with a 1-0 win at Hanover as Kosovo striker Milot Rashica scored the winner by finishing off a move started by captain Max Kruse.
Stuttgart remain in the relegation places after a 3-2 defeat at home to Mainz.
Mainz built up a 3-0 lead with an own goal by Stuttgart defender Santiago Ascacibar before striker Jean-Philippe Mateta and defender Alexander Hack netted.
However, Stuttgart roared back with two goals in the final seven minutes from Nicolas Gonzalez and Marc Oliver Kempf before Anastasios Donis hit the post in a dramatic finish.
Fortuna Duesseldorf, who last month stunned Dortmund 2-1 and drew 3-3 at Bayern, are now six games unbeaten after a 2-1 win at Augsburg with Benito Raman scoring the winning goal in the 90th minute.Frankfurt fly high
Leverkusen 0 M'gladbach 1
Stuttgart 2 Mainz 05 3
Frankfurt 3 Freiburg 1
Augsburg 1 Dusseldorf 2
Hanover 0 Werder 1
Investigators say the attackers had received significant amounts of cash and cryptocurrency from Ukraine
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