In two sustained, controlled spells, the fast bowler tore through the top-order of the tourists' batting yesterday to finish with five for 33 -- his sixth five-wicket innings haul in Test cricket.
Jerome Taylor joined in the rout with two wickets, including captain Mushfiqur Rahim to keep the pressure on the beleaguered Bangladeshis.
Only Tamim Iqbal offered any sustained resistance on a pitch that continues to offer assistance to the fast bowlers. He got to 48 before edging a probing delivery from Roach to wicketkeeper Denesh Ramdin.
Shivnarine Chanderpaul was the fulcrum of the home side's batting effort in the first half of the day, compiling an unbeaten 84 as the wickets fell around him once the fourth-wicket partnership with Darren Bravo was broken after an hour's play.
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Displaying greater discipline on a helpful pitch than on the first day, the Bangladesh seamers reaped considerable reward in the morning session.
Al-Amin Hossain claimed two wickets in two balls after Robiul Islam had Bravo caught at the wicket for 46.
Chanderpaul continued to soldier along at his very serene pace to his 65th Test half-century, being overshadowed by the big-hitting Taylor who blazed 40 in a 54-run eighth-wicket stand before finding Mahmudullah on the long-on boundary off the bowling of left-arm spinner Taijul Islam.