Cross-Chain Transaction Tracking in 2025

The Multi-Chain Challenge

The cryptocurrency ecosystem has evolved from Bitcoin-only to a complex multi-chain landscape with dozens of active blockchains. Criminals exploit this complexity by moving funds across chains to evade detection. In 2024, over $2.3 billion in illicit funds crossed blockchain bridges, making cross-chain tracking a critical skill for forensics professionals.

Understanding Blockchain Bridges

Bridges enable asset transfers between blockchains through various mechanisms:

Lock-and-Mint Bridges

• Mechanism: Assets locked on source chain, wrapped tokens minted on destination
• Examples: Wormhole, Multichain, Synapse
• Tracking: Monitor lock events on source chain and mint events on destination
• Identifiers: Bridge transaction IDs link source and destination transactions

Liquidity Pool Bridges

• Mechanism: Swap assets from pools on both chains
• Examples: Hop Protocol, Across Protocol, Stargate
• Tracking: More complex due to liquidity pooling
• Challenge: Funds may not have direct 1:1 correspondence

Atomic Swaps

• Mechanism: Direct peer-to-peer exchange using hash time-locked contracts
• Examples: Atomic DEX, Komodo
• Tracking: Requires identifying matching HTLCs on both chains
• Privacy: More difficult to track due to decentralized nature

Cross-Chain Tracking Techniques

1. Bridge Event Monitoring

Track bridge-specific events to link transactions across chains:

• Lock Events: Identify when assets are locked on source chain
• Mint Events: Find corresponding wrapped token minting
• Burn Events: Track when wrapped tokens are burned
• Unlock Events: Identify when original assets are released
• Transaction IDs: Use bridge-specific identifiers to link transactions

2. Wrapped Asset Analysis

Understanding wrapped assets is crucial for cross-chain tracking:

• WETH (Wrapped ETH): ERC-20 version of ETH for DeFi compatibility
• WBTC (Wrapped BTC): Bitcoin on Ethereum, backed 1:1 by BTC
• Bridge-Specific Wraps: Each bridge may create its own wrapped version
• Tracking: Monitor wrap/unwrap events to follow fund flow
• Custodians: Identify who holds the underlying assets

3. Timing Analysis

Use temporal patterns to link cross-chain transactions:

• Bridge Latency: Typical time for bridge transactions (5-30 minutes)
• Amount Correlation: Match transaction amounts across chains
• Sequential Patterns: Identify chains of bridge transactions
• Batch Processing: Some bridges process transactions in batches

Major Blockchain Ecosystems

Ethereum and EVM Chains

• Ethereum: Primary DeFi hub, most liquidity
• Polygon: Ethereum sidechain with lower fees
• BSC: Binance Smart Chain, high transaction volume
• Avalanche: Fast finality, growing DeFi ecosystem
• Arbitrum/Optimism: Layer 2 scaling solutions

Non-EVM Chains

• Bitcoin: Original blockchain, limited smart contract capability
• Solana: High-speed chain with unique architecture
• Cosmos: Inter-blockchain communication protocol
• Polkadot: Multi-chain network with parachains
• Cardano: Research-driven blockchain with eUTXO model

Common Cross-Chain Money Laundering Patterns

Chain Hopping

Criminals move funds across multiple chains to obscure the trail:

• Pattern: ETH → BSC → Polygon → Avalanche → back to ETH
• Purpose: Break analysis tools that focus on single chains
• Detection: Track bridge transactions and timing patterns
• Indicators: Rapid sequential bridge usage, round-trip patterns

Bridge + Mixer Combination

Combining bridges with mixing services for maximum obfuscation:

• Pattern: Bridge to new chain → Mix → Bridge back
• Example: ETH → Tornado Cash → Bridge to BSC → Mix on BSC → Bridge back
• Challenge: Breaks direct transaction links
• Approach: Focus on amounts, timing, and behavioral patterns

Wrapped Asset Swaps

Using wrapped assets to move between chains without obvious bridge transactions:

• Pattern: BTC → WBTC on Ethereum → Bridge WBTC to Polygon
• Advantage: Can use DEXs instead of centralized exchanges
• Tracking: Monitor wrap/unwrap events and bridge transactions

Case Study: Ronin Bridge Hack ($625M)

The Ronin Network bridge hack in March 2022 is the largest bridge exploit to date:

• Attack: Compromised validator keys to approve fraudulent withdrawals
• Stolen Assets: 173,600 ETH and 25.5M USDC
• Cross-Chain Movement: Funds bridged from Ronin to Ethereum
• Laundering: Mixed through Tornado Cash, converted to BTC
• Attribution: Linked to North Korean Lazarus Group
• Recovery: Some funds frozen at exchanges, partial recovery achieved

This case demonstrates the importance of monitoring bridge transactions and the challenges of cross-chain fund recovery.

Tools for Cross-Chain Tracking

• Multi-Chain Explorers: Blockchair, Blockchain.com for multiple chains
• Bridge Aggregators: LI.FI, Socket for tracking bridge routes
• Forensics Platforms: Elliptic, TRM, ForensicBlock with multi-chain support
• DEX Aggregators: 1inch, Paraswap for tracking cross-chain swaps
• Portfolio Trackers: Zapper, DeBank for following addresses across chains

Best Practices

• Map the Journey: Create a visual diagram of cross-chain movements
• Track All Variants: Monitor wrapped, bridged, and native versions of assets
• Use Multiple Tools: Different platforms have different chain coverage
• Understand Bridge Mechanics: Each bridge works differently
• Monitor Bridge Contracts: Set up alerts for large or suspicious bridge transactions
• Collaborate: Share findings with investigators on other chains
• Document Everything: Maintain detailed records of cross-chain links